rewrite `topo_scale.py` using barebone Dask

[ArcticSnow]

The topo_scale.py routine currently works well for small project, but quickly runs into trouble when used for larger projects. The internal computation of topo_scale could be improved and re-imprelemented using pure Dask syntax in order to limit the intermediate computation and memory usage.

TODO:

• figure Dask usage
• seek potential Dash user
• identify bottleneck of current method

This will justify a new release version